Verified answer

Showing the internal mechanics (though they may not have been logical at all) was a trademark of the 70's mecha material. However, for Gundam, I think the most "official" early version of this would be the "cutaway" model kit (I've provided the link below).

However, the more "official" internals would whichever is the latest model kit with full internals. In this case, I would say that the Perfect Grade 1/60 Model Kit may provide the most "physically official" version of the internal mechanics. Link is also included below.